Summary Brown University requests support for a FEI Teneo VS variable pressure Scanning Electron Microscope (SEM) for serial block face imaging in the life sciences. Ultrathin sections are cut inside the microscope and series of images are acquired from the freshly cut block face, while the sections are discarded. The automated system is capable of imaging large z-stacks at isotropic 10x10x10 nm resolution. The series of images can be processed for 3D reconstruction of cells and tissues, with sufficient resolution to identify small vesicles, organelles and neural connections. The user group requested the basic Teneo VS system. This system includes equipment essential for serial block-face imaging and 3D reconstruction of the data sets, but does not include additional features or accessories. The requested system will replace a 25-year old SEM in the Division of Biology and Medicine at Brown University. The Teneo VS will be the only SEM in the Division of Biology and Medicine and the only variable pressure SEM for serial block-face imaging in the State of Rhode Island. The microscope will be used immediately by 15 investigators at Brown University and Rhode Island Hospital for high-resolution 3D imaging of cellular and sub-cellular structures ranging from germ plasm in embryos to neural circuits in the retina. Collectively, these 15 users are funded by 26 NIH grants. The Major Users have a substantial need for the requested SEM for serial block-face imaging. As an indication of this substantial need, all Major Users have obtained preliminary results with various out- of-state SEMs for serial block-face imaging. While these preliminary results demonstrate the Major User group's need and expertise, the major users had limited access to the SEMs for serial block-face imaging and could only image a subset of samples that were important to their research programs. The Minor Users were unable to gain access to SEMs for serial block-face imaging, but have research projects that would immediately benefit from the proposed equipment. The impact of the proposed imaging system will extend beyond the projects of the Major and Minor Users, since the microscope will be made be made available to the broader scientific community in Rhode Island, which has more than 600 active NIH-funded projects with a total annual budget of $184 million. The microscope will be set up in the Leduc Bioimaging Facility at Brown University, which has the technical expertise to maintain the instrument, train its users and provide consultation on planned and ongoing research projects. In addition, the users will have access to assistance in sample preparation and data analysis. The Leduc Bioimaging Facility, supported by a broadly-based Advisory Committee, has an excellent track-record maintaining various high-end imaging systems and has strong institutional support, which guarantees that the instrumentation will be used to its maximum potential for years to come.